Tuning screw having a double choke



Mardi 17, 1964 c. E. WARD 3,125,734

TUNING SCREW HAVING A DOUBLE cHoxE Filed April s, 19Go United States Patent O 3,125,734 TUNING SCREW HAVING A DOUBLE CHOKE Curtis E. Ward, Los Altos, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Apr. 6, 1960, Ser. No. 20,330 7 Claims. (Cl. 33383) This invention relates generally to ultra high frequency electromagnetic apparatus and more particularly to a novel non-contacting tuning apparatus for utilization in wave propagating structures or external tuning cavity resonators for klystrons and the like.

Tuning assemblies now exist wherein tuning rods extend into the waveguides or cavity resonators without contacting the walls of the waveguide, the tuning rod being movably supported at a pointremoved from the place of entrance into the waveguide'. For mechanical rigidity and vibrationless operation, however, it is desirable that at least two long-wearing bearing supports for the tuning rod be utilized, provided, however, that no metal-to-metal contacts occur at any portion of the assembly which carries R.F. current and which therefore could produce R.F. noise in the waveguide.

It is, therefore, the object of the present invention to provide a novel vibrationless, long-wearing, smooth tuning, non-contacting tuning assembly constructed so as 'to eliminate all sources of metal-to-metal contact or bearing surfaces along the RF. current carrying portions of the assembly.

One feature of this invention is the provision of a novel tuner assembly having a capacitive tuning rod that makes no metal-to-metal contact with the waveguide or cavity resonator and which is supported in the tuner assembly in a manner such that there is no metal-to-metal Contact at any portion of the assembly which carries RF. current.

A further feature of the present invention is the provision of a tuner assembly of the above featured type having a novel lower and upper choke system which provides a radio frequency short circuit between the capacitive tuner rod and the waveguide or cavity resonator without metal-to-metal contact.

Still a further feature of the present invention is the provision of a non-contacting, double choke, capacitive tuner probe assembly using a dielectric sleeve in the lower choke as a radially loaded bearing having no metalto-metal contact with the tuner rod and a combination of graphited cast iron against stainless steel as an upper threaded bearing to accomplish axial motion for the tuner rod having very long life.

These and other objects and advantages will become apparent from a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal cross section view of a tuner assembly embodying the present invention,

FIG. 2 is a partial cross sectional view of the lower choke and dielectric sleeve taken at 2 2 in FIG. 1,

FIG. 3 is a perspective view of the lower choke and FIG. 4 is a view of the present tuner assembly utilized in the external cavity resonator of a tunable klystron oscillator.

Referring now to FIGS. l through 4, one embodiment of the present invention is shown mounted on a cavity resonator although it should be noted that the tuner may be utilized in other microwave circuits such as waveguides. The cavity resonator body 1 is centrally apertured and counterbored from the top, the aperture 1 providing for the admission of a capacitive tuning rod 3 into the inner chamber 4 of cavity resonator 1. The diameter of the capacitive tuning rod 3 is smaller than the 3,125,734 Patented Mar. 17, 1964 ice central aperture 1 so that there will be no metal-tometal Contact between the inner wall of cavity resonator 1 and capacitive tuning rod 3. Located in the counterbore of cavity resonator 1 is a radio frequency lower choke 5 formed by a hollow cylinder 5 made of, for example, silver plated steel having a anged bottom portion 5, the ilange portion 5 of lower choke 5 nestling in the base of the counterbore of cavity resonator 1. Dielectric sleeve 6 made of, for example, Teflon is closely tted inside of lower choke cylinder 5' and acts as a bearing in which tuning rod 3 moves. A flange 6' is provided for dielectric sleeve 6 to prevent dielectric sleeve 6 from slipping down inside of lower choke cylinder 5.

An upper choke 7 is formed by a counterbored hollow cylinder 7' provided with an outer shoulder 7, which is also tted into the counterbore of cavity resonator 1 making metal-to-metal contact with flange 5" of lower choke cylinder 5. The inner step of the counterbore of upper choke cylinder 7 is adapted to accommodate liange 6 of dielectric sleeve 6. A rubber gasket 8 is tted between the external wall of cavity resonator 1 and external shoulder 7" of upper choke cylinder 7 to permit hermetic sealing of the resonant cavity if so desired. The inner diameter of upper choke cylinder 7 is larger than the diameter of capacitive tuning rod 3 so that there is no metal-to-metal contact between upper choke cylinder 7 and capacitive tuning rod 3. Capacitive tuning rod 3 is held in position in dielectric sleeve 6 by deforming lower choke cylinder or member 5 and dielectric sleeve 6 such as to crimp inward at three places to obtain an approximate triangular shape so that when capacitive tuning rod 3 is forced into inner cavity chamber 4 through upper choke 7, dielectric sleeve 6, and lower choke 5, the deformed triangular shape of dielectric sleeve 6 will exert a radial resilient load on capacitive tuning rod 3.

The outer shoulder 7 of upper choke cylinder 7 accommodates the counterbore step of a two-stepped, hollow, counterbored tuner mounting sleeve 9 made of, for` example, stainless steel. The upper portion of tuner` mounting sleeve 9 is internally threaded and has a small outwardly protruding lip 9', and the lower portion of mounting sleeve 9 has an apertured ilange for accommodating bolts 18 for fastening mounting sleeve 9 to cavity resonator 1.

A tuner assembly 10, made of graphite cast iron and having a central bored out lower portion for accommodating the upper end of tuning rod 3 by force fit, is provided to relate movement of tuner rod 3 into cavity chamber 4. This movement is accomplished through a threaded external lower portion of tuner assembly 10 mating with the internal threaded portion of tuner mounting sleeve 9. A metal spring clamp 16 is provided around the exterior of theV threads to keep a radial load on the threads. A slot 10' is cut in the top of tuner assembly 10 to accommodate a screw driver for rotating tuner assembly 10. This rotation, when transmitted to the threaded portion of tuner assembly 10, provides longitudinal movement to the tuning rod 3. A built-in felt oiler` 11 is provided to lubricate the threaded surfaces of tuner assembly 10 and tuner mounting sleeve 9. A silicone grease is used in felt oiler 11 as silicone grease is generally uneffected by temperature changes. The graphited cast iron of tuner assembly 10 in conjunction with the stainless steel threads of tuner mounting sleeve 9 and the silicone grease in felt oiler 11 accomplish unusually long and low friction thread life. The long wearing properties are due to graphite particles and iron particles from tuner assembly 10 smoothing both the threaded surface of tuner mounting sleeve 9 and the running surfaces of tuner assembly 10. The graphite particles and iron particles are held in position by the silicone grease which of itself is a relatively poor lubricant. The combination of graphited cast iron of tuner assembly l@ running against stainless steel threads of tuner mounting sleeve 9 gives a factor of 1t) improvement in life over, for example, stainless steel running against stainless steel. The felt oiler 11 is held in position around tuner assembly by seals 12 and 13. A rubber O-ring 14 is fitted around tuner assembly 16 for hermetic sealing of the tuner assembly.

The threaded portion of tuner mounting sleeve 9 forms the upper bearing for the tuner assembly and is protected from dirt and dust particles by housing 1S, a metal cylinder having an inward flange 1S at the top and an apertured flange outwardly at the bottom. The inward flange of the top of housing 15 along with metal seal 13 provides a housing for rubber O-ring 14 while lower flange of housing 15 is apertured for accommodating bolts 19 to secure housing 1S to tuner mounting sleeve 9. Bolts 19 are fitted through apertures in the lower flange of housing 15 and are secured into taps drilled into tuner mounting sleeve 9. A rubber gasket 17 is provided be tween the lower end of housing 15 and tuner mounting sleeve 9 for hermetic sealing. The tuning rod 3 is supported at two places, the upper bearing or threaded por tion of tuner assembly 10 and tuner mounting sleeve 9 and by the radially loaded lower bearing consisting of lower choke cylinder 5' and dielectric sleeve 6. As lower choke cylinder 5 is deformed into triangular shape as best seen in FIG. 3, it springs radially to accommodate varying diameter of tuning rod 3 without allowing play in the lower bearing and, since the lower bearing is dielectric, there is no variable metal-to-metal contact to become noisy when tuning or noisy due to wear caused by tuning.

Operation of the no-metal-contacting double choke capacitive cavity tuner is as follows: The upper end of lower choke 5 extends 1A: wavelength from the upper wall of the resonant cavity 4, this upper end being an open circuit by virtue of the physical short circ-uit at its lower end created by the ange 5" interconnecting the lower choke cylinder 5 and the lower end of upper choke cylinder 7. The open circuit at the upper end of lower choke 5 is reflected a distance of M4 to provide an R.F. short circuit between rod 3 and upper wall of cavity 4. This lower choke 5 is backed up by upper choke 7 which operates in the same manner as described -for the lower choke, the physical short circuit occurring at the upper surface of the shoulder 7" and the sleeve 9. By the use of this combination of an R.F. short between the wall of cavity 4 and capacitive tuner rod 3 and the lower and upper choke system, RF. energy will not leak up into the threaded portion of the tuner assembly causing noise to be reflected back into the cavity chamber.

lIn FIG. 4, the novel tuner assembly is shown mounted on the external tunable cavity resonator 21 of a known type of internal-external cavity resonator reiiex klystron 22., this tuner providing substant-ially llonger life for the external cavity than previous tuners.

Since many changes could be made in the above construction and many -apparently widely different embodiments of this invention could -be made without departing from the scope thereof, it is intended that all matter contained in the above `description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

-1. A high frequency tuning apparatus for varying the electrical characteristics of a wave propagating structure comprising a tuning rod movably extending into the wave propagating structure `through an aperture in the wall thereof without contacting the wall to elect tuning therein and support means for supporting said tuning rod on said wave propagating structure, said support means including a lower bearing formed by a dielectric sleeve and an upper bearing :formed by a tuner mounting sleeve threadably mating with screw threads on said tuning rod whereby a frictional bearing is -obtained between the mating threaded portions of the upper bearing and a sliding bearing is obtained at said lower bearing, a resilient choke member encircling said rod and serving to form a choke for said tuning rod and also serving to hold said dielectric sleeve in position around said tuning rod, and a second choke member encircling said rod and serving to form a second choke along said tuning rod and between the iirst choke and the upper bearing.

2. A thigh frequency tuning apparatus as claimed in claim l wherein said tirst choke member comprises an out-of-round metallic cylinder.

3. A high frequency tuning apparatus as claimed in claim l wherein the screw threads on said tuning rod are made of graphited cast iron and the threaded tuner mounting sleeve is of steel.

4. A high frequency tuning apparatus as claimed in claim l wherein said dielectric sleeve bearing is provided with a flange positioned at a point between said tirst and second choke members.

5. A high frequency tuning apparatus as claimed in claim 4 wherein said second choke member comprises a multidiameter cylindrical member including a shoulder between the inner and outer diameters, the smaller diameter portion of said multidiameter cylindrical member serving with said tuner mounting sleeve to form the second choke, the shoulder of said multidiameter cylindrical member being positioned on `the ilange of said dielectric sleeve bearing, the larger diameter portion of said second choke member surrounding said iirst choke member in a spaced-apart manner thereby `defining the outer portion of said lower choke.

6. A high frequency tuning apparatus for varying the electrical characteristics of a wave propagating structure comprising, a tuning 4rod movably extending into the wave propagating structure through an aperture in the wall thereof without contacting the wall to eiect tuning therein, said aperture having a co-unterbore portion therein, a cylindrical member positioned in the base of the counterbored portion of the aperture in said cavity resonator, a ilanged dielectric sleeve positioned within said cylindrical member, said dielectric sleeve providing a lower hearing means for supporting said tuning rod on said wave propagating structure, a multidiameter ycylindrical member including an inner and outer shoulder, the greater diameter portion of said multidiameter cylindrical member positioned in the base of the aperture in `said wave propagating structure surrounding said cylindrical member in a spaced-apart manner, the inner shoulder positioned on the ilanged portion of said dielectric member and the smaller diameter portion of said multidiameter cylindrical member surrounding said tuning rod in a spaced-apart manner, and a tuner mounting sleeve threadably mated with screw threads on said tuner rod whereby a rictional upper bearing is obtained between the mating threaded portions of the sleeve and rod, a portion of said tuner mounting sleeve surrounding the smaller diameter portion of said multidiameter cylindrical member in a spacedapart manner and positioned on the outer shoulder of said multidiameter cylindrical member whereby said upper and Ilower bearings support said tuning rod, said cylindrical member serves with the greater diameter portion of said multidiameter member to form -a lower choke for said tuning rod, and the `smaller diameter portion of said multidiameter cylindrical member serves with said tuner mounting sleeve portion to form an upper choke for said tuning rod.

7. A tuning apparatus as claimed in claim 6 wherein the first cylindrical member comprises -an out-of-round metallic cylinder for resiliently pressing said dielectric sleeve against said tuning rod.

(References on following page) 6 References Cited in the le of this patent 3,016,501 Gardner Jan. 9, 1962 UNITED STATES PATENTS 3,045,146 Haegele Illl'y 17, 1962 2,351,895 Allerding June 20, 1944 OTHER REFERENCES 2,451,876 Salisbury Oct. 19, 1948 2,853,678 Tomiyasu Sept23195g 5 Ragan: Mxcrowave Transmission Circuits, Radia'uon 2,946,027 Gerard et aL July 19, 1960 Laboratory Series, vol, 9, copyright 1948, pages 487-488. 

1. A HIGH FREQUENCY TURNING APPARATUS FOR VARYING THE ELECTRICAL CHARACTERISTICS OF A WAVE PROPAGATING STRUCTURE COMPRISING A TUNING ROD MOVABLY EXTENDING INTO THE WAVE PROPAGATING STRUCTURE THROUGH AN APERTURE IN THE WALL THEREOF WITHOUT CONTACTING THE WALL TO EFFECT TUNING THEREIN AND SUPPORT MEANS FOR SUPPORTING SAID TUNING ROD ON SAID WAVE PROPAGATING STRUCTURE, SAID SUPPORT MEANS INCLUDING A LOWER BEARING FORMED BY A DIELECTRIC SLEEVE AND AN UPPER BEARING FORMED BY A TURNER MOUNTING SLEEVE THREADABLY MATING WITH SCREW THREADS ON SAID TURNING ROD 